Manual Trans rebuild info and bearing specs

Thought I'd post up a bunch of specs and info on rebuilding the manual trans. Be nice to have all the recommended clearances and as many part numbers as possible to help makes things easier and quicker to reference. All info comes from various dsm gurus and copied posts from the tooners, dsmtalk, and ecmlink forums. I plan on adding to this as I come across relevant info.

For the higher HP numbers, I would run a higher preload. Personally on mine, (AWD), I am running FWD style tapered roller bearings with 0.010" preload on my front diff.

If someone is looking at this thread for preload/endplay information for an AWD front differential utilizing standard roller bearings NOT tapered roller bearings, you must use ENDPLAY on the bearings to prevent thrust loading the bearings. Use a range of 0.000"-0.005" ENDPLAY on AWD front differentials. OEM spec is 0.003"-0.005".

For reference, FWD transmissions get bearing preload on ALL shafts, no matter what the OEM manual tells you. All shafts use tapered roller bearings, so preload ANY tapered roller bearing.

For reference, AWD transmissions get bearing preload on the input shaft, intermediate shaft, output shaft and center differential while having endplay on the front differential, no matter what the OEM manual tells you about putting endplay on the input shaft. We preload the input shaft as high as 0.007-0.012", and the intermediate shaft in the 0.009-0.015" range.

The more preload on the input shaft, the better ability it will give you in slowing the transmission down to shift better at higher rpm and putting less stress on the synchro and the clutch assembly.

The more preload on the intermediate shaft, the better ability it will have in reducing thrust-loading and pushing away the shaft from the input shaft resulting in improper gear mesh and risk of gear tooth/shaft failure.

The more heat in the transmission, the more the case will thermally expand, reducing preload on the shafts. If the transmission is in a high-temperature environment, adding a transmission cooler will help, and higher preloads are recommended to help the transmission shift good at 200+ degrees.

The solder trick is an easy way of finding out the gap between the bearing race and the case. Remove the bearing race and old shim, then place the bearing race on top of the differential bearing, then use some lube or grease to hold the solder in place. Use 0.062" diameter electrical rosin core solder and cut two pieces approximately 1/2" to 3/4" long and gently bend them into a curve matching the bearing race curvature and place these two pieces evenly spaced across from each other on top of the bearing race. Then, reinstall the case section and torque the bolts down to 29 ft/lbs.

Remove case bolts, remove case section, and you should have two evenly flat pieces that you can take measurement from to get the bearing preload for your FWD transmission.

Using either an accurate digital caliper or a micrometer, measure the thickness of the two pieces of solder. They should be close in thickness. If they are unevenly squished or way off in thickness, redo until you get evenly squished/close thickness measurements. Once you have two decent thicknesses, add the two thicknesses together and divide by two to get an average thickness. This number will be your "zero" preload/endplay value. To add preload, you will add around .007" to your calculated number to get a preload of .007" on your FWD front differential tapered roller bearings.

cheekychimpDirector of Housing and Urban Development, and carbon/kevlar balls

posted 02/26/15 10:48 PM

Opinions are always going to vary on the "ultimate" ratio, and in addition your own view will likely change depending upon your application.

I have a rare "unicorn" 4.3 final ratio transmission from an ex-rally car that is an absolute blast to drive. 1st through 4th are short ratio but 5th gear doesn't appear any shorter than stock given that my rpm at given speeds match what I routinely saw on 3.545 and 3.909 ratio transmissions. Logically however this must be achieved by a different combination of ratios. It is superb around town, on twisty back roads and especially on hill climbs.

At some point it will also need a rebuild. 5th to 4th down changes grind if performed quickly, so it has to be babied a bit. When I eventually get round to that I will give what information I can on the guts. I've been putting it off because the box is matched to the rear end (obviously) and we have absolutely no idea what is inside. The box will have to be removed, opened and examined with a view to identifying parts, then most likely the parts will need to be ordered (another 2-4 week wait at best assuming no unicorn parts are involved). Either it goes back together whilst we wait for parts or it is off the road for 6 weeks minimum.

For drag racing I do know that a GGSX and JDM 3.909 ratio hybrid box actually produces ratios that are almost identical to Magnus' Dogmission trans. However it is most likely far weaker and may not stand up to any genuine drag strip abuse. I always thought it would be a cool 'highway' transmission but I also like having a rear LSD and the GGSX ring and pinion doesn't fit over a standard EVO III/VR4 rear diff. For drag racing that's probably not an issue but you are still back to the strength problem.

Regarding ratios in general, there are two files (Excel I think) that you might find useful. One is a conversion application that allows you to input various primary and secondary ratios to obtain top speeds in various gears, the other is just a table that gives you the final ratio and corresponding speeds in each gear for various combinations of VR4, DSM and GGSX transmission parts. Because of the Excel format it is difficult to post the tables in their native format here, however, if you are interested, shoot me a PM (with your email) and I can send them to you.